Growth control of SV40 virus transformed 3T3 (SV3T3) cells will be studied. The proposed investigations include: studies on the regulation of essential amino acid transport by serum factors and cAMP; the characterization of quiescent SV3T3 cells cultured in leucine deficient medium; the study of mechanisms which are involved in the regulation of the cell cycle of normal and malignant cells; the purification of a serum factor that is toxic for malignant cells. The project is designed to find conditions that arrest the growth of SV3T3 cells without damaging normal 3T3 cells in order to understand how to restore normal growth patterns in malignant cells. Also, the studies are seeking new ways to selectively eliminate cancer cells without damaging normal cells by manipulating the nutritional conditions (nutrients, growth stimulatory or toxic serum factors) in the culture medium. Some of the proposed studies might lead to a possible practical application of methods to selectively kill some malignant cells.